他在这家公司任经理已经三年了。

Tā zài zhè jiā gōngsī rèn jīnglǐ yǐjīng sān nián le.

He has served as a manager in this company for three years.

他曾任我们学校的校长。

Tā céngrèn wǒmen xuéxiào de xiàozhǎng.

He once served as the principal of our school.

他在大学里任中文老师。

Tā zài dàxué lǐ rèn Zhōngwén lǎoshī.

He works as a Chinese teacher at the university.